For example, because of the limited radio resources, the number of network operators who can have a frequency license is limited. Those who do not have the frequency license may lease equipments such as a radio base station to provide mobile communications services. Thus, operators who do not necessarily own equipments such as radio base stations, networks or the like, but still provide mobile communications services by leasing them from mobile network operators (MNOs) who actually own those equipments to execute mobile communications services such as cellular phones are called mobile virtual network operators (MVNOs).
WiMAX Forum which is the standard committee that defines common specifications of radio system based on the IEEE802.16 standard establishes a network reference model (WiMAX Forum Network Architecture).
In the WiMAX Forum's network reference model, networks are classified into network access providers who are operators providing a radio access to mobile stations, and network service providers who provide an internet protocol (IP) access to mobile stations.
As one example of embodiments for MVNO, MNO may be designated as a network access provider in the WiMAX Forum network reference model, and MVNO may be designated as a network service provider in the WiMAX Forum network reference model.
[Patent Document 1] Japanese Patent Laid-open Publication No. 2008-035037
[Patent Document 2] Japanese Patent Laid-open Publication No. 2004-187282
However, in a network apparatus (hereinafter, referred to as a gateway) which interconnects a network of an MNO with a network of an MVNO, it is necessary to execute communications having a closed area property between a device (mobile station) of a user that executes a network access and the MVNO with which the user enters into a contract. That is, at an initial access of a mobile station, user authentication needs to be performed between the mobile station and an authentication server which is managed by the MVNO with which the user enters into a contract. In addition, when the mobile station executes communications with a network, it is necessary to transmit a packet sent from the mobile station only to the network of the MVNO with which the user enters into a contract.